1. Field of the Invention
The present invention relates to an optical semiconductor module used in fiber optic communications to converge light emitted from a semiconductor light-emitting device and couple it into an optical fiber.
2. Description of the Related Art
Improvement in light coupling efficiency, simplification in construction, and uniformity in axial length are becoming important considerations in designing optical semiconductor modules used in fiber-optic communications so as to converge light emitted from a semiconductor light-emitting device and couple it into an optical fiber.
In a known optical semiconductor module, a semiconductor light-emitting device containing a laser diode is assembled in a cap-like holder together with a rod-like lens, and a ferrule in which an optical fiber is mounted is inserted in a receptacle. The receptacle and holder are connected together by a cylindrical ring so that the light emitted from the semiconductor light-emitting device is focused onto the light receiving end of the optical fiber.
An optical semiconductor module having such a construction is fabricated in the following manner. First, a semiconductor light-emitting device and a lens are inserted into a holder which in turn is inserted into a ring. Then, a ferrule in which an optical fiber is mounted is inserted into a receptacle. After the holder, ring, and receptacle are assembled together, the holder and ring are moved axially relative to each other for positional alignment before the joint between them is welded by laser. Similarly, the ring and receptacle are moved relative to each other along their adjoining faces and then welded together by laser. Such an optical semiconductor module is disclosed, for example, in Japanese Laid-Open Patent Publication No. 3-233415.
In the known optical semiconductor module, as described above, three parts, i.e., the holder, ring, and receptacle, are needed to hold the semiconductor light-emitting device, lens, and optical fiber in place. Furthermore, the relative position between the semiconductor light-emitting device and the lens are determined permanently once they have been assembled into the holder. It has therefore been necessary to adjust the distance between the receptacle and the holder by adjusting the joining position between the holder and the ring so that the light emitted from the semiconductor light-emitting device can be focused onto the light receiving end of the optical fiber. Since the overall axial length of the module has to be varied, this has presented a problem as it causes variations in the outer dimensions of the module.